Precise Twist Angle Determination in Twisted WSe 2 via Optical Moiré Phonons

Twisted bilayers of transition metal dichalcogenides (TMDC) form moiré superlattices hosting localized excitons and enabling access to Mott-Hubbard physics by the formation of moiré minibands. However, their electronic properties are highly sensitive to twist angle fluctuations, disorder, and lattice reconstructions, making fast and noninvasive local characterization challenging. Here, we correlate twist angle variations in twisted WSe2 bilayers across micrometer length scales using lateral force microscopy (LFM) and micro-Raman spectroscopy. We reveal twist angle variations exceeding 1° across optically and transport-relevant length scales. For twist angles in the range 3° < α < 12°, distinct Raman signatures from optical moiré phonons enable high-precision twist angle determination with sub-micrometer spatial resolution under ambient conditions. Our approach achieves a precision better than ± 0.3° particularly in the low-twist angle regime relevant for correlation physics and is applicable to hBN-encapsulated heterostructures, establishing micro-Raman spectroscopy as a rapid, noninvasive tool for twist angle screening.